Traditional preservation and storage of biologics, such as cells and biomolecules, usually involves special storage media, refrigeration, liquid nitrogen storage, or a highly specialized buffer solution. These biologics are usually used in a short period of time after their preparation to prevent spoilage due to the natural process of degradation and risks of pathogen contamination. For example, anucleated cells, such as platelets, have a shelf life at room temperature of only about 5 to 7 days. In addition, nucleated cells such as reproductive cells (Dinnyes et al., Reprod. Fertil. Dev., 2007, 19, 719-31), stem cells (De Sousa et al., Reproduction, 2006, 132, 681-9) and hepatocytes (Bakala et al., Pol. J. Vet. Sci., 2007, 10, 11-8) must be maintained in expensive storage devices and possess limited shelf-life at room temperature.
There have been several attempts to extend the shelf life of cells. Some of these methods are reported in, for example, U.S. Pat. Nos. 7,150,991; 7,135,180; 7,094,601; 6,841,168; 6,723,497; 6,770,478; 5,827,741; and 5,629,145; and in the following literature: Puhlev et al., Cryobiology, 2001, 42, 207-17; Ma et al., Cryobiology, 2005, 51, 15-28; Matsuo, Br. J. Ophthalmol., 2001, 85, 610-2; McGinnis et al., Biol. Reprod., 2005, 73, 627-33; Gordon et al., Cryobiology, 2001, 43, 182-7; Bhowmick et al., Biol. Reprod., 2003, 68, 1779-86; Meyers, Reprod. Fertil. Dev., 2006, 18, 1-5; Chen et al., Cryobiology, 2001, 43, 168-81; Wolkers et al., Cryobiology, 2001, 42, 79-87; Crowe et al., Arch. Biochem. Biophys., 1983, 220, 477-84; Chen et al., Cryobiology, 1993, 30, 423-31; and U.S. Pat. No. 6,528,309.
Current technologies of cell preservation often focus on freeze-drying as a means for preserving cells in the dry state. Freezing cells, however, can promote ice crystal formation as well as osmotic changes during the process and result in disruption of intracellular organelles and membranes, resulting in loss of cells (i.e., transient warming effect) or loss or significant diminution of cell functions. Further, freeze-drying can, and often does, result in generating microparticles that are apparently formed from the cellular debris. As pointed out from a report involving various freezing protocols for hepatocyte suspensions, mostly devastating results such as low recovery and severe loss of functions occurred (Koebe et al., Chem. Biol. Interact., 1999, 121, 99-115). In another report, experiments showed that a mechanical interaction between ice crystals and red blood cell membrane induced mechanical damage to the membrane (Ishiguro et al., Cryobiology, 1994, 31, 483-500).
Thus, in many instances, the current protocols for preserving and/or storing biologics, whether via lyophilization, freeze-drying, vacuum dry and/or oven dry methods, are not sufficient to dry cells and to recover desired functions upon reconstitution. As can be immediately recognized, there is a need in the art for preservation and/or storage alternatives to extend shelf life of biologics for therapy, diagnostics and research. Accordingly, the present invention provides methods of preserving and/or storing biologics to preserve cell structures and functions in the dried or semi-dried states. These processes can result in cells that will recover full or partial function upon reconstitution and rehydration.